A variety of prior art devices are currently known for echo control in voice communication systems. Two distinct types are generally classed as echo cancellers and echo suppressors. An echo canceller generally comprises two primary components, a transversal filter for modeling the impulse response of an associated echo path and an algorithmic unit which determines the filter coefficients and adapts them to achieve agreement with the echo path. Generally, such echo cancellers are operated in an adaptive mode and they monitor the state of traffic and echo conditions more or less continuously. The filters employed generally utilize many stages of delay. This requires the generation and updating of many multiplication coefficients and a large multiplication and accumulation cycle count during a real time operation. Implementing such a device requires powerful signal processing computation equipment and is generally more costly, though much more effective, than the aforementioned simple echo suppressor.
An echo suppressor is a relatively inexpensive and simple device that consists basically of a switch for interrupting the echo return path and decision logic for determining when to operate the switch. Essentially, such devices operate on a detected threshold of activity to sense that local speech traffic is being generated and then utilize this fact to interrupt or to suppress the echo path. Real time high power computational requirements are eliminated but significant clipping of voice traffic, as is well known in the art, oft times results.